Storage system, backup system, and backup method

ABSTRACT

A storage controller can perform backup processing without proceeding via a server and without the need for the server to grasp the state of pair volumes. When an instruction for backup is given from the server while data is being copied from a source volume to a target volume, the storage controller transfers the data to a backup device using differential information between the pair volumes after waiting until data about a range to be backed up and instructed by the server is copied into the target volume.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of application Ser. No.10/784,999, filed Feb. 25, 2004, now U.S. Pat. No. 7,114,046, andrelates to and claims priority from Japanese Patent Application No.2003-183742, filed on Jun. 27, 2003, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the backup of informationstored in a storage system, and, more particularly, to server-freebackup of information on a storage area network (SAN).

As computer systems have treated an increasing amount of information inrecent years, there is an increasing need for backing up suchinformation. Thus, there is a tendency for the load imposed on backupprocessing of a server to be increased. Where a server backs up a largeamount of data, the data is read from a storage system with which asource storage device to be backed up is connected, and then the data iswritten into a target backup device, such as a tape library, forexample.

However, as the amount of data increases, the server resources (e.g.,host bus adapter) used for the backup are occupied for a longer time.Thus, if another application program tries to use this host bus adapterto send and receive other data during this interval, the processing hasto wait for a long time or the performance deteriorates greatly.

One means for alleviating the burden imposed on a server's backupprocessing to solve the above-described problems involves the backup ofdata using an Extended Copy command.

On the other hand, in an application where there is a large amount ofI/O processing to and from a storage volume, in a case where the serverissues a splitting instruction to pair volumes, an update copy from thesource volume to the target volume may not be immediately ended. Rather,some time is taken until a split state is reached. To solve thisproblem, there is a technique that is available. In particular, when aserver issues a splitting instruction to pair volumes, a storagecontroller continues an update copy to the target volume, whileresponding to the server that the pair volumes are in a split state.

Patent Reference 1: JP-A-2001-222355

Patent Reference 2: JP-A-2002-366310

However, where data is transferred to a backup device that is differentfrom the server, it is only assured that the data in the storage devicewill be transferred to the server. Therefore, the consistency betweenthe data transferred from the target volume to the backup device and thedata in the source volume is not assured.

Furthermore, if a backup is performed after waiting until data to beupdated is completely reflected in the target volume from the sourcevolume, the server waits without being capable of giving an instructionfor start of backup processing until the data to be updated iscompletely reflected in the target volume. The server needs to monitorthe split state.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide atechnique which makes it possible to respond to a server that pairvolumes are in a split state. The technique also assures consistency ofdata even in a case where the data is transferred to a backup deviceusing a backup command, and it enables backup without urging theserver's processing to wait.

A storage system that achieves this object has a storage controller anda storage device. The storage controller has a memory, together withfirst, second, third, and fourth control portions. The storage devicehas first and second storage units. The first control portion of thestorage controller stores information into the first storage unit viathe memory. The control portion that actually stores information intothe storage unit is the third control portion. The first storage unit isa source volume. The second storage unit is a target volume.Furthermore, the third control portion stores information from the firststorage unit into the second storage unit.

On the other hand, when an instruction for pair splitting is given fromthe server, the storage controller writes differential informationbetween the first and second storage units into the memory. Also, thepair splitting is reported to the first server. Then, where a backupcommand is subsequently received from the second server, the fourthcontrol portion transfers data to be backed up to a backup device basedon the differential information between the pair volumes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a client server, a backup server, and astorage system;

FIG. 2 is a diagram showing a table on a common memory necessary tocheck backup processing and differential data between pair volumes, aswell as a data storage area;

FIG. 3 is a conceptual block diagram of a first embodiment;

FIG. 4 is a flowchart of the processing carried out in the firstembodiment;

FIG. 5 is a conceptual block diagram of a second embodiment;

FIG. 6 is a flowchart of the processing carried out in the secondembodiment;

FIG. 7 is a conceptual block diagram of a third embodiment;

FIG. 8 is a conceptual block diagram showing a modification of the thirdembodiment;

FIG. 9 is a flowchart of the processing carried out in the thirdembodiment;

FIG. 10 is a conceptual block diagram of a fourth embodiment; and

FIG. 11 is a flowchart of the processing carried out in the fourthembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be hereinafter with reference to thedrawings.

First Embodiment

FIG. 1 is a diagram showing the configuration of a storage system 300 ina first embodiment of the present invention. In the storage system 300,a storage controller 301 is connected with a client server 101 via aswitch 304 by paths 201 and 206, and it controls I/O processing requiredfrom the client server 101. Similarly, the storage controller 301 isconnected with a backup server 102 via the switch 304 by paths 202 and203, and it controls I/O processing required from the backup server 102.Furthermore, the storage controller 301 is connected by paths 204 and205 via the switch 304 with a tape device 303, that constitutes a backupdevice, and it controls I/O processing to and from the tape device 303.The client server 101, backup server 102, storage controller 301 andbackup device 303 are connected via the switch 304. The switch 304controls the route of the paths. For example, when the client server 101issues a command to a channel port 401, the command sent from the clientserver 101 via a path is analyzed in terms of the destination address bythe switch 304. The shortest route is selected and the command isrouted. In this case, the command reaches the channel port 401 via thepath 206.

The client server 101 and backup server 102 are connected by the LAN206. The servers 101 and 102 communicate with each other to control theparameters/timing of commands of pair split and instruction commands forbackup. The pair splitting commands and instruction commands for backupare issued from backup software 105 and 106, and they are sent to thestorage controller 301 via drivers 103 and 104, respectively. Theprocessing of the client server 101 and backup server 102 may beperformed all by the client server 101. Conversely, the backup server102 may perform all of the processing of the client server 101.

The storage controller 301 has I/O processing control portions (I/Oprocessors) 501-503 for performing I/O processing with the client server101 and backup server 102 via the channel ports 401-403. Also, thestorage controller 301 has an I/O processing control portion (I/Oprocessor) 508 for performing I/O processing with volumes. The, I/Oprocessors 501-503 and 508 can operate independently. For example, the1/O processor 501 performs I/O processing from the client server 101. Onthe other hand, the I/O processor 508 independently performs I/Oprocessing between a common memory/cache memory 507 and a storage device302. The common memory/cache memory 507 is a memory that can be accessedfrom the I/O processors 501-503.

The I/O processors 501-503 and 505 have individual memories 504-506 and509, respectively, that store respective control information. Theseindividual memories cannot be accessed from plural I/O processors. Incontrast, the common memory/cache memory 507 can temporarily store datafrom servers and data from the storage device 302, as well as controlinformation that can be shared among the I/O processors 501-503 and 508.

The storage device 302 that is connected with the storage controller 301has a source volume 601, a target volume 602, a volume 603 for pairoperation, and a volume 604 for backup processing. The I/O processor 508directly performs I/O processing on each volume of the storage device302. For instance, where the I/O processor 501 writes Write data fromthe client server 101 into the source volume 601, the I/O processor 501once stores the Write data into the common memory/cache memory 507. Atthis stage, the I/O processor 501 reports completion of writing to theclient server 101. Then, the I/O processor 501 performs other I/Oprocessing. Meanwhile, the I/O processor 508 performs polling- atregular intervals on the common memory/cache memory 507. Where the Writedata is stored in the common memory/cache memory, the I/O processor 508writes the Write data into the source volume 601. Because of theabove-described I/O processing, I/O processing including reading andwriting is performed between the client server 101 and source volume601.

When the source volume 601, in which the data in the client server 101has been stored, is backed up to the tape device 303, it is necessary tocreate a copy of the source volume 601 into the target volume 602 withinthe storage device 302, because if the storage controller 301 attemptsto perform a backup from the source volume to the tape device directly,the I/O processing from the client server 101 that is normal processingbecomes deteriorated. Alternatively, it is necessary to stop the I/Oprocessing.

The source volume 601 and target volume 602 that form a pair of volumescan take the following states:

(1) Simplex state: A pair of a source volume and a target volume is notformed.

(2) Duplex pending state (transient duplex state): After a source volumeand a target volume form a pair, creation copy processing and updatecopy processing are carried out or might be carried out. The creationcopy process referred to herein involves a copy of data from the sourcevolume to the target volume and occurs when a copy of data from thesource volume to the target volume is started, but both are not yet in afully mirrored state. On the other hand, the update copy processinvolves a copy of data from the source volume to the target volume andoccurs when data is written into the source volume either before thesource and target volumes assume a fully mirrored state or after theyhave reached a fully mirrored state.

(3) Duplex state: After source and target volumes form a pair, thecreation copy process is complete, and the source and target volumes arein a fully mirrored state. However, an update copy of data from thesource volume to the target volume might be carried out.

(4) Split state: This is a state obtained after the pair of source andtarget volumes has been split.

(5) Split pending state (transient split state): After the pair ofsource and target volumes has been split, differential data that is tobe updated from the source volume to the target volume still exists. Anupdate copy process is carried out.

A copy process can be performed from a source volume to a target volumeby making transitions between the above-described states. In the presentembodiment, assignments to the source volume 601 and target volume 602are stored in source volume number 512 and target volume number 513 ofthe common memory/cache memory 507 shown in FIG. 2. Furthermore, abackup processing-and-management area 510, that is managed by the commonmemory/cache memory 507, has the following: backup parameter information511 for storing parameter information about a backup, source volumenumber 512, target volume number 513, pair volume difference information514, pair state information (source volume) 516, and pair stateinformation (target volume) 517. In addition, the cache memory has abackup data storage area 515 for storing backup data read from aspecified area. The pair state information (source volume) 516 and pairstate information (target volume) 517 are available as means for knowingwhether differential data is reflected or not. If a pair split isperformed, the pair state information (source volume) 516 immediatelybecomes “pair split”, but the pair state information (target volume) 517remains in “transient pair split” state until the differential data isreflected in the target volume. Therefore, it is possible to knowwhether the differential data has been reflected, from this-information,the storage controller 301, and servers 101, 102.

FIG. 3 is a conceptual block diagram illustrating a summary of thebackup processing in the present embodiment. For the sake of simplicity,the switch 304, I/O processors 501-503, 508, etc. are omitted in FIG. 3.The storage controller 301 is a conceptual diagram of backup processingin a case where differential data from the source volume 601 to thetarget volume 602 exists after the pair volumes have been split. If aninstruction command for backup is issued from the backup server 102after the pair splitting, the storage controller 301 checks to see ifdifferential data remains in the range to be backed up. Wheredifferential data remains, the storage controller 301 reflects thedifferential data concerning the portion to be backed up in the targetvolume 602 and then transfers the backed-up data to the tape device 303.This permits the processing to proceed without producing a wait time inthe backup processing.

FIG. 4 is a flowchart illustrating a summary of the processing carriedout in the present embodiment. It is assumed that a creation copy orupdate copy is made from a source volume to a target volume. (1) Thebackup server 102 issues an instruction command for starting a backup tothe client server 101. (2) The client server 101 receiving the commandissues an instruction command for splitting the pair volumes to the I/Oprocessor 501. Then, the I/O processor 501 causes the pair stateinformation (source volume) 516 to pair split. (3) Also, the I/Oprocessor 501 reports the end of the splitting of the pair volumes tothe client server 101. In this state, pair state information (targetvolume) 517 is in a pending pair split state. Subsequently, theprocessor 501 issues a command to the processor 508 based on the pairvolume difference information 514 to perform a copy of data from thesource volume to the target volume. The I/O processor 508 receiving thecommand executes a copy of data into the target volume 602 according tothe pair volume difference information 514 that manages the data notreflected from the source volume 601 to the target volume 602 at theinstant of the pair splitting, until the data in the source volume 601agrees with the data in the target volume 602. Here, the processor 508operates independently of the processing of the processors 501-503.

Meanwhile, (4) the client server 101 receiving the report of the end ofthe splitting reports the completion of the splitting of the pairvolumes to the backup server 102. (5) The backup server 102 receivingthe report of the completion of the splitting of the pair volumes issuesan instruction command for backup to the I/O processor 502. Theprocessor 502 receiving the instruction command for backup analyzes thebackup instruction command and stores the results of the analysis in thebackup parameter information 511. An example of this backup parameterinformation includes parameters of an Extended Copy command that is aSCSI standard. Volume information about the source volume, volumeinformation about the backup destination, and information describing therange backed up are contained in the parameters. Then, an instructioncommand for the backup is reported to the processor 503. Here, the I/Oprocessors 502 and 503 are assigned to two I/O processors and the I/Oprocessing is performed to distribute the load. Also, the channel portsare divided into two, i.e., channel ports 402 and 403, to secure thecommunication bandwidth for the paths.

The I/O processor 503, upon receiving the Backup instruction commandfrom the I/O processor 502, checks the pair volume differenceinformation 514 to confirm whether all of the range to be backed up oreach unit of data to be written into the backup device has been copiedfrom the source volume 601 to the target volume 602 by referring to thebackup parameter information 511. Where the differential data about therange to be backed up does not exist in the pair volume differenceinformation 514, the processor 503 reads data to be backed up from thetarget volume into the cache memory. Then, backup to the tape device 303is started. Meanwhile, (6) where the I/O processor 503 refers to thebackup parameter information 511 and the differential data about therange to be backed up is present in the pair volume differenceinformation 514, the I/O processor 503 gives an instruction to the I/Oprocessor 508 to copy the differential data. The I/O processor 508receiving the instruction performs a copy operation with a priority onthe differential data about the range to be backed up. After thecompletion of the copy operation, the I/O processor 508 reports thecompletion of the copy of differential data about the range to be backedup to the I/O processor 503.

(7) The I/O processor 503 receiving the report backs up the data aboutthe range to be backed up to the tape device 303. After completion ofthe backup, the processor 503 reports the end of the backup to theprocessor 502. (8) The processor 502, upon receiving the report of theend, reports the end of the backup to the backup server 102, thus endingthe backup.

After the end of the backup, the I/O processor 508 continues to copyuntil a duplex state is reached, i.e., the source and target volumesagree in data content.

The present embodiment makes it unnecessary for the backup server 102 towait for pair splitting of the target volume 602. Furthermore, thebackup server 102 does not need to monitor the state of the pair splits.Hence, the load on the backup server 102 can be reduced.

Second Embodiment

FIG. 5 is a conceptual block diagram of backup processing in accordancewith a second embodiment. After pair splitting, if the backup server 102issues an instruction command for backup, the storage controller 301checks to see if differential data remains in the range to be backed up.Where differential data remains, the I/O processor 503 makes the backupcommand wait until all the differential data has been copied into thetarget volume 602. As a result, it takes a long time until the backupprocessing is completed, but the processing in the storage controller301 is made simpler. In addition, the backup processing can be made toproceed without the client server 101 and backup server 102 monitoringthe state of the target volume 602.

FIG. 6 is a flowchart illustrating a summary of the processing. Theprocessing is almost identical with the first embodiment. The differencefrom the first embodiment is that the I/O processor 503 monitors thestate of reflection of the differential data between the pair volumesand starts backup processing after all of the differential data has beenreflected in the target volume.

FIG. 7 shows a modification of the present embodiment, illustratingprocessing in a case where the backup software 106 for the backup server102 monitors the differential data, instead of the storage controller301 in FIG. 5. In FIG. 5, after pair splitting, the source volume 601 ofthe pair of volumes quickly assumes a state of “pair split”. On theother hand, the target volume 602 remains in the “pending-split state”until all of the differential data is reflected in the target volume.Therefore, it is impossible to perform backup processing. However, thebackup server 102 can check to see whether or not the differential datais reflected in the target volume 602. Therefore, the serverperiodically checks the state. After confirming that the “pair splitstate” has been reached, the backup server 102 can issue a Backup Startcommand. In this modified embodiment, the backup server 102 can controlthe backup processing instead of monitoring the state of the targetvolume 602 by the I/O processor 503.

Third Embodiment

FIG. 8 is a conceptual block diagram illustrating the manner in whichbackup processing is performed using the backup data storage area 515 ina case where differential data exists from the source volume 601 to thetarget volume 602 after the pair volumes have been split in backupprocessing.

After pair splitting, if an instruction command for backup is issuedfrom the backup server 102, the storage controller 301 checks to seewhether differential data remains in the range to be backed up. Wheredifferential data remains, the storage controller 301 reads thedifferential data concerning the portion to be backed up from the sourcevolume 601 and once stores the data into the backup data storage area515. Furthermore, if the data about the range to be backed up has beenreflected in the target volume 602, the data is read into the backupdata storage area 515 and merged with the data from the source volume601. Then, the merged data is transferred to the tape device 303. Thus,even where there is differential data in the same way as in the firstembodiment, the processing can be made to proceed without producing await time in the backup processing. Since differential data is notreflected in the target volume 602, the backup processing can beperformed at a correspondingly higher rate.

FIG. 9 represents a flowchart illustrating a summary of processing inthe present embodiment. The processing in the present embodiment isalmost identical with the first embodiment. The differences are asfollows. Where the I/O processor 503 checks the state of reflection ofthe differential data between the pair volumes and finds that the datais not reflected, data is read from the source volume 601 to the backupdata storage area 515. After data about the range to be backed up isfully read into the backup data storage area 515, the I/O processor 503transfers data about the range to be backed up to the tape device 303.Meanwhile, where data about the range to be backed up all exists in thetarget volume, the I/O processor 503 reads the data about the range tobe backed up from the target volume 602 into the backup data storagearea 515 and then transfers the data to the tape device 303. Where thedifferential data is not reflected in the target volume, data is storeddirectly into the backup data storage area 515 without writing the datainto the target volume 602 by this method and so data about the range tobe backed up can be prepared quickly.

Fourth Embodiment

FIG. 10 is a conceptual block diagram illustrating processing in a casewhere a Pair Splitting instruction command and a Backup instructioncommand are combined into one command in backup processing. In thepresent embodiment, the client server 101 does not need to issue a PairSplitting instruction command, unlike the aforementioned embodiments.Instead, the backup server 102 first reports the start of a backup tothe client server 101 via the LAN 205. Because of this report, theclient server 101 temporarily interrupts normal I/O processing andresponds to the backup server 102 regarding the start of the backup. Thebackup server 102 subsequently issues a Backup instruction command tothe storage controller 301 without monitoring the paired state of thevolumes. On receiving the Backup command, the storage controller 301gives an instruction for canceling the first specified paired state. Atthis instant, the controller responds to the Backup command. The backupserver 102 receives the response from the storage controller 301 andmakes a report for resumption of I/O processing to the client server101. After receiving the report, the client server 101 resumes the I/Oprocessing.

Meanwhile, the storage controller 301 that has given an instruction forpair splitting then reflects the differential data about the range to bebacked up in the target volume 602 and transfers the backed-up data tothe tape device 303. Because the backup server 102 monitors the state ofthe backup in the storage controller, the backup server 102 can know theend of the backup. For example, the backup server 102 checks the stateby issuing a command for checking the status of backup processing, suchas a Receive Copy Result command, to the storage controller 301.

FIG. 11 represents a flowchart illustrating the processing of FIG. 6summarily. The backup server 102 issues an instruction command forstarting a backup to the client server 101. The client server 101receiving the Backup Start instruction interrupts the normal I/Oprocessing temporarily. The normal I/O processing is interrupted becausethe processing for splitting the pair volumes is performed quickly. Theclient server 101 that has temporarily interrupted the I/O processingreports the interruption to the backup server 102. The backup server 102receiving the report issues an instruction command for splitting pairvolumes to the I/O processor 502. The I/O processor 502 receiving theBackup instruction command issues an instruction command for splittingpair volumes to the I/O processor 508. Then, the I/O processor 508performs processing independently of the I/O processors 502 and 503 inthe background and copies differential data into the target volume.

Meanwhile, the I/O processor 502 brings the pair state information(source volume) 516 into a pair split state and brings the pair stateinformation (target volume) 517 into a pending split state and thenreports the end of the splitting to the backup server 102. Furthermore,the I/O processor 502 makes a report of the Backup instruction commandto the I/O processor 503. Where the differential data about the range tobe backed up does not exist in the target volume, the I/O processor 503reflects the differential data about the range to be backed up from thesource volume to the target volume. Then, the I/O processor 503transfers the data about the range to be backed up to the tape device303. Other processing is almost identical with the processing in thefirst embodiment.

In the present embodiment, backup processing can be performed withoutfor the client server 101 or backup server 102 monitoring the state ofthe pair volumes.

In the present embodiment, in a case where the data concerning the rangeto be backed up is not reflected in the target volume, the I/O processor503 stores the data into the backup data storage area 515, and then itcan transfer the data to the tape device 303. Furthermore, the I/Oprocessor 503 can make the transfer to the tape device 303 wait untilthe differential data is fully copied into the target volume.

While the invention made by the present inventor has been described indetail based on various embodiments, it is obvious that the invention isnot limited to the above-described embodiments, but can be modifiedvariously without departing from the gist thereof.

For example, in accordance with the present invention, a LAN is used asthe network between the client server 101 and backup server 102. Thenetwork is not limited to a LAN. It may also be a fiber channel,telephone network, wireless network, or the like.

In addition, in accordance with the invention, the I/O processor 508 isused for processing on the storage device 302. For this I/O processing,the I/O processors 501-503 can be used.

Furthermore, in accordance with the invention, the volume 603 for pairoperation and the volume 604 for backup processing can be defined on thecommon memory/cache memory without using actual volumes.

Additionally, in accordance with the invention, the backup device is notlimited to the tape device 303. It may also be another type of storagedevice, such as a disk device.

Further, in accordance with the invention, the client server 101 andbackup server 102 can be combined into one server. Also, instead of aserver, a host can be used.

According to the present invention, one can obtain the advantage thatbackup processing from a server can be performed after responding to theserver that pair volumes have been split and maintaining the consistencyin data between source and target volumes.

1. A storage system comprising: a first storage unit for storinginformation from a first server; a second storage unit for storing theinformation stored in said first storage unit; and a storage controllerbeing coupled with said first storage unit, said second storage unit,said first server, and a second server, and being used to control saidfirst storage unit and said second storage unit, wherein when aninstruction for splitting is received from said first server, saidstorage controller reports end of the splitting to said first server,receives an instruction for backup from said second server, and thentransfers information to a backup device from said second storage unitafter copy of information from said first storage unit to said secondstorage unit ends, wherein a state of differential data is checked,wherein if the differential data exist representing that backup data isnot reflected in the second storage unit, then data within a range to bebacked up is fully read and transferred to the second storage unit andthen transferred to a tape device serving as the backup device, andwherein if the differential data does not exist representing that alldata within the range to be backed up is reflected in the second storageunit, then the data is read from the second storage unit and transferredto the tape device.
 2. A storage system as set forth in claim 1, whereindata is transferred from said second storage unit to said backup deviceafter copy of all data from said first storage unit to said secondstorage unit ends.
 3. A backup method for a storage system having afirst storage unit for storing data from a first server, a secondstorage unit for storing the data stored in said first storage unit, anda storage controller being connected with said first storage unit, saidsecond storage unit, said first server, and a second server, and beingused to control said first storage unit and said second storage unit,wherein said method comprising the steps of: causing said first serverto issue an instruction for splitting between said first and secondstorage units to said storage controller; then causing said storagecontroller to report an end of the splitting to said first server beforecompleting of copying from said first storage unit to said secondstorage unit; and then, when an instruction for backup is received fromsaid second server during the copying from said first storage unit tosaid second storage unit, transferring data from said second storageunit to a backup device after the end of copy of the data from saidfirst storage unit to said second storage unit based on controlling bysaid storage controller, checking state of differential data, wherein ifthe differential data exist representing that backup data is notreflected in the second storage unit, then data within a range to bebacked up is fully read and transferred to the second storage unit andthen transferred to a tape device serving as the backup device, andwherein if the differential data does not exist representing that alldata within the range to be backed up is reflected in the second storageunit, then the data is read from the second storage unit and transferredto the tape device.
 4. A backup method as set forth in claim 3, whereinwhen there is a request from said second server for transfer of datastored in said second storage unit to the backup device, the data istransferred to said backup device from said second storage unit afterend of copy of the whole data into said second storage unit from saidfirst storage unit.
 5. A backup method for a storage system having afirst storage unit for storing data from a first server, a secondstorage unit for storing the data stored in said first storage unit, anda storage controller being connected with said first storage unit, saidsecond storage unit, said first server, and a second server, and beingused to control said first storage unit and said second storage unit,wherein said method comprising the steps of: causing said first serverto issue an instruction for splitting between said first and secondstorage units to said storage controller; then causing said storagecontroller to report an end of the splitting to said first server beforecompleting of copying from said first storage unit to said secondstorage unit; and then, when an instruction for backup is received fromsaid second server during the copying from said first storage unit tosaid second storage unit, transferring data from said second storageunit to a backup device after the end of copy of the data from saidfirst storage unit to said second storage unit based on controlling bysaid storage controller, when there is a request for transfer of firstinformation stored in said second storage unit and second informationnot stored in said second storage unit from said second storage unit tothe backup device, copying said first information from said secondstorage unit into a memory that is connected with said storagecontroller and acts to store information and said second information iscopied directly from said first storage unit into said memory, and saidfirst information and said second information stored in said memory aretransferred to said backup device.
 6. A backup system comprising:servers for storing data; a first storage unit for storing data fromsaid servers; a second storage unit for copying the data stored in saidfirst storage unit; and a storage controller connected with saidservers, said first storage unit, and said second storage unit andcontrolling said first and second storage units; wherein when saidstorage controller receives an instruction for splitting between saidfirst and second storage units from said servers, an end of splitting isreported to said servers before completing of copying from said firststorage unit to said second storage unit, an instruction for backup isreceived from said servers during the copying from said first storageunit to said second storage unit, then data is copied from said firststorage unit into said second storage unit, and after the end thereofthe data is transferred from said second storage unit to the backupdevice based on controlling by said storage controller, wherein a stateof differential data is checked, wherein if the differential data existrepresenting that backup data is not reflected in the second storageunit, then data within a range to be backed up is fully read andtransferred to the second storage unit and then transferred to a tapedevice serving as the backup device, and wherein if the differentialdata does not exist representing that all data within the range to bebacked up is reflected in the second storage unit, then the data is readfrom the second storage unit and transferred to the tape device.
 7. Abackup system as set forth in claim 6, wherein said servers have a firstserver for issuing the instruction for splitting and a second server forissuing the instruction for backup.
 8. A backup system as set forth inclaim 6, wherein information is transferred from said second storageunit to said backup device after copy of whole data from said firststorage unit to said second storage unit ends.
 9. A backup systemcomprising: servers for storing data; a first storage unit for storingdata from said servers; a second storage unit for copying the datastored in said first storage unit; and a storage controller connectedwith said servers, said first storage unit, and said second storage unitand controlling said first and second storage units; wherein when saidstorage controller receives an instruction for splitting between saidfirst and second storage units from said servers, an end of splitting isreported to said servers before completing of copying from said firststorage unit to said second storage unit, an instruction for backup isreceived from said servers during the copying from said first storageunit to said second storage unit, then data is copied from said firststorage unit into said second storage unit, and after the end thereofthe data is transferred from said second storage unit to the backupdevice based on controlling by said storage controller, when there is arequest for transfer of first information stored in said second storageunit and second information not stored in said second storage unit fromsaid second storage unit to the backup device, said first information isstored from said second storage unit into a memory that is connectedwith said storage controller and acts to store information and saidsecond information is stored directly from said first storage unit intosaid memory, and then said first information and said second informationstored in said memory are transferred to said backup device.
 10. Astorage system comprising: a plurality of storage units; and a storagecontroller for controlling said storage units, wherein said storageunits include first and second storage units, and wherein said storagecontroller comprises; (a) a memory, (b) a first control portionconnected with said memory, accepting splitting processing between saidfirst and second storage units sent from a first server, and reportingan end of the splitting to said first server before completing ofcopying from said first storage unit to said second storage unit, (c) asecond control portion connected with said memory and accepting backupprocessing sent from a second server after said report of the end of thesplitting during the copying from said first storage unit to said secondstorage unit, (d) a third control portion connected with said storageunits and said memory, and acting to copy data from said first storageunit to said second storage unit, and (e) a fourth control portionconnected with said memory and transferring data from said secondstorage unit to a backup device after the end of copy of data from saidfirst storage unit to said second storage unit based on controlling bysaid storage controller, wherein a state of differential data ischecked, wherein if the differential data exist representing that backupdata is not reflected in the second storage unit, then data within arange to be backed up is fully read and transferred to the secondstorage unit and then transferred to a tape device serving as the backupdevice, and wherein if the differential data does not exist representingthat all data within the range to be backed up is reflected in thesecond storage unit, then the data is read from the second storage unitand transferred to the tape device.
 11. A storage system as set forth inclaim 10, wherein data is transferred from said second storage unit tosaid backup device after end of copy of whole data from said firststorage unit to said second storage unit.
 12. A storage systemcomprising: a plurality of storage units; and a storage controller forcontrolling said storage units, wherein said storage units include firstand second storage units, and wherein said storage controller comprises:(a) a memory, (b) a first control portion connected with said memory,accepting splitting processing between said first and second storageunits sent from a first server, and reporting an end of the splitting tosaid first server before completing of copying from said first storageunit to said second storage unit, (c) a second control portion connectedwith said memory and accepting backup processing sent from a secondserver after said report of the end of the splitting during the copyingfrom said first storage unit to said second storage unit, (d) a thirdcontrol portion connected with said storage units and said memory, andacting to copy data from said first storage unit to said second storageunit, and (e) a fourth control portion connected with said memory andtransferring data from said second storage unit to a backup device afterthe end of copy of data from said first storage unit to said secondstorage unit based on controlling by said storage controller, when thereis a request for transfer of first information stored in said secondstorage unit and second information not stored in said second storageunit from said second storage unit to the backup device, said firstinformation is stored from said second storage unit into a second memoryconnected with said storage controller and acting to store informationtemporarily and said second information is stored directly from saidfirst storage unit into said second memory, and wherein said firstinformation and said second information stored in said second memory aretransferred to said backup device.